Whatever the application, effective operation of belt conveyors depends on mechanical and physical properties, size and shape of the loads handled. The larger the lumps a belt conveyor of a given design can accommodate and the faster the belt speed, the higher the effect of the equipment in operation. This is particularly true in the mining and building industries.
There is known, for example, a belt conveyor (cf. Rotec Creter Crane-125-24; Parts and Maintenance, Operation Instructions, Assembly and Safety; Rotec Industries, Inc.) incorporating an endless belt, a drive and a frame. A plurality of medial idlers flanked by inclined side idlers of the cantilever type at either end are fitted to the frame one next to the other. Top side idlers are provided at the sides of the belt sabstentially at right angles to a plane therethrough and in contact therewith to train the belt correctly apart from the medial and side idlers.
Giving speedy and effective service, this design is not free, however, from some shortcomings. It cannot handle large lumps because the top side idlers hamper their progress and because the impact loads they impose on the medial, side and top side idlers are detrimental to the integrity of the idlers lacking a shock-absorbing mounting. In training the belt along the axis of the conveyor, the top side idlers bear upon the belt edge within a narrow area of contact. The resultant unit load is high, bringing about ply separation and slipping of the belt, wear on top side idlers.
Not excluded is the possibility of ill-training the belt. It may result accidentally if, for example, the dirt or dust entering some of the bearings impedes the rotary motion of the idlers they support. Ill-training of the belt can also be caused by an out-of-square of idlers relative to the axis of the conveyor due to inaccurate installation of the conveyor. The known design is deprived of any means of controlling the path of the belt when the conveyor is in operation and train the belt accurately along the axis thereof so that the function of the top side idlers would be a standby one.
In practice, the training of the belt is accomplished in the following way. On spotting a malfunctioning idler which causes belt misalignment, the conveyor is stopped and the material it carries is unloaded. The faulty idler is turned through an angle in plan the magnitude whereof is selected by the person in charge subjectively, on the basis of his skill and experience. Commonly, this angle is 1.degree.-3.degree. as measured from a plane at right angles to the axis of the belt in the clockwise direction if the belt travels away from the point of observation and tends to misalign to the left. The idler turned as indicated interacts with the belt resiliently slipping past it and gives rise to a force which is applied to the belt and tends to displace this in the direction opposite to the direction of misalignment, bringing at balance the force which has caused the ill-training of the belt. However, the arbitrarily selected angle of turn and a possible mistake in identifying the exact idler causing the misalignment commonly render this method of control useless. Since no additional ways of controlling the training of the loaded belt on the go exists in this case, as this was pointed out above, the top side idlers contacting the belt edges are the last resort in spite of their rapid wear and ply separation of the belt.
Also known is a belt conveyor of another design (cf. USSR Inventor's Certificate No. 346,192; IPC B 65 g 21/04; dated Dec. 21, 1970) incorporating a study framework and at least two pliable load-carrying members of considerable length which are tensioned, extend inside the framework essentially parallel to each other and to the axis of the conveyor and are linked to said framework so as to be supported in a given position. The framework is also provided with a means of tensioning said pliable load-carrying members. A plurality of medial rolling means are located between the pliable members substantially at right angles thereto and are spaced a distance apart from one another along the conveyor. A plurality of fulcrum pins are located substantially at right angles to the pliable members so that their supporting ends are connected to the pliable members with provision for displacing integrally therewith in the vertical and horizontal planes. The fulcrum pins are disposed on either side of said pliable members externally thereto and spaced a distance apart from one another. They carry a plurality of side rollers. A plurality of linking means the number whereof equals that of the fulcrum pins is also provided for. The linking means are rods located substantially parallel to the fulcrum pins and rigidly attached each to the respective side rolling means (idler) and to the pliable member as well. Each linking means is also pivoted to the sturdy framework with one of its ends, whereby the pivoted joint between this linking means and the framework is located at the inward side of the respective pliable member below a plane through these members. The belt conveyor also incorporates an endless belt and a belt drive.
These features of the design enable the conveyor to handle large lump material at a speed not less than ever before. The rolling means (idlers) are so attached to both the framework (frame) and the pliable members that they can yield under impact loads, greatly reducing thereby the effect of these loads on components of idlers and frame. But there is evidence that belt training appears to be a problem in this case.
The recourse to top side idlers is hardly practicable, for it will limit the size of lump material handled due to reasons given above.
The tendency of the belt for ill-training seems to be unavoidable. It can be spurred spontaneously by a sluggish operation of a group of idlers due to dust in their bearings no matter how accurately these idlers have been fitted at right angles to the axis of the belt. The pliable members which are commonly steel wire ropes are likely to elongate in operation due to strain relaxation under tensile loads with the result that idlers, especially those at the sides, get out-of-true in plan and create favourable conditions for belt-misalignment forces to come into play. Since the linking means are located at the inward sides of the pliable members below a plane therethrough, the side idlers can yield under impact loads but the troughing of the belt decreases when the pliable members displace downwards. With the diminishing of the amount of troughing of the belt, the pressure the side idlers exert on the belt decreases and so does the tilt of these idlers. Thus conditions are created which facilitate belt misalignment. During a spontaneous occurence of the event, the pressure sustained by the side idlers towards which the belt displaces increases and that coming on the opposite side idlers decreases. The side idlers, being connected through the linking means to the pliable members which deform directly with the load they sustain, tilt at the side displacing towards which is the belt at a lesser degree than at the opposite side. Such positioning of the side idlers invites difficulties for the belt to return into alignment with the conveyor axis.
The known design also creates no prospect of controlling the position of side idlers when the belt is carrying load. An arbitrary adjustment of their position can be made only on stopping the conveyor. Therefore, accurate training of the belt is a formidable problem in operating the known conveyor.
Large and medium lumps of the material carried can collide with side idlers, causing these to deflect and vibrate. The amplitude of the vibration increases with the height of idlers so that the lumps contacting idler tops get an acceleration high enough for them to bounce off the belt.
It is an object of the invention to provide a belt conveyor of a design capable of conveying bulk and sticky building materials or large lump rock owing to an ability of the side rolling means to yield.
Another object of the invention is to ensure accurate belt training.
A further object of the invention is to create conditions permitting positional control of the rolling means to be exercised when the belt is on the go.